Fungus-assisted mild acid pretreatment of Glycyrrhiza uralensis residues to enhance enzymatic hydrolysis and oil production by green microalga Chlorella protothecoides

The potential of fungal pretreatment prior to acetic acid pretreatment using Phanerochaete chrysosporium for enzymatic hydrolysis and algal oil production from Glycyrrhiza uralensis residue (GUR) was investigated. After co-pretreatment with P. chrysosporium and acetic acid, the loss of lignin and holocellulose was 47.4% and less than 28%, respectively. Subsequently, the acid insoluble residues were further hydrolyzed with cellulase into fermentable sugars, and then used for heterotrophic cultivation of Chlorella protothecoides for bio-oils production. The concentration of reducing sugars in enzymatic hydrolyzate from co-treated GUR was 1.62 times as that of solely acid pretreated GUR. The maximum yield of algal biomass and oil from co-pretreatment (4.46 and 1.91 g/L) were both higher than those from sole acid pretreatment. Thus, this study demonstrated the feasibility of using reducing sugars obtained from enzymatic hydrolysis of GUR co-treated with P. chrysosporium and acetic acid as substrate for oil production.